/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/NiagaraGraph.h
Walk through the graph for an ParameterMapGet nodes and see if any of them specify a default for VariableName.
void MultiFindParameterMapDefaultValuePins ( TConstArrayView< [FName](API\Runtime\Core\UObject\FName) > VariableNames, [ENiagaraScriptUsage](API\Plugins\Niagara\ENiagaraScriptUsage) InUsage, [ENiagaraScriptUsage](API\Plugins\Niagara\ENiagaraScriptUsage) InParentUsage, [TArrayView](API\Runtime\Core\Containers\TArrayView)< [UEdGraphPin](API\Runtime\Engine\EdGraph\UEdGraphPin) * > DefaultPins ) const